E4-v3 forensic: structural d-to-p-sync.jsonl is empty despite the
sweep passing --enable-d-to-p-sync. Root cause:
BenchmarkLiveConfig (benchmark.py) had no enable_d_to_p_sync field,
and the benchmark-live cli builder (line ~821) never threaded
args.enable_d_to_p_sync into the ReplayConfig that gets built
inside replay_trace. So config.enable_d_to_p_sync was always False
even though the CLI flag was set, and _attempt_d_to_p_sync was
gated off → 0 calls → 0 RPCs → 0 structural log entries.
The replay subcommand (cli.py:672) already plumbed it correctly;
benchmark-live just got missed. Adding the field + the wire-up.
This means E4-v3's headline numbers (KVC v2 + load-floor + RDMA
beat naive PD on mean/p50/p90, lose by ~8% on p99) reflect *only*
KVC's session-affinity gains, not D→P. A v4 with this fix should
exercise D→P on reseed-after-eviction events and we'll see whether
the p99 long tail also shrinks.
Implements the design proposed and approved in
docs/E1_E2_FIX_DESIGN_ZH.md §Q2.B.
KvAwarePolicy gains a `load_floor_bonus: int = 0` knob. When > 0:
mean_assigned = sum(assigned[*]) / len(D)
for each D candidate:
if not sticky and mean_assigned > 0:
deficit = max(0, mean_assigned - assigned[D])
floor_bonus = K * deficit / mean_assigned
else:
floor_bonus = 0
score = (overlap + sticky*α + floor_bonus, sticky, -inflight, -assigned)
Properties (verified by unit-style probe in commit message):
- Default 0 = old behavior preserved
- Sticky-gated: turn-1+ requests of an existing session keep going
to their original D (cache locality preserved)
- Graduated: bonus magnitude scales with the D's deficit ratio,
approaches K as deficit/mean → 1, drops to 0 when balanced
- Set above max expected boilerplate overlap (Inferact ~50 → 200)
so cross-session shared-prefix overlap doesn't pin cold D's idle,
but real per-session prefix overlap (>K blocks) still wins
Plumbed through ReplayConfig, BenchmarkConfig, and CLI flag
--kvcache-load-floor-bonus on both `replay` and `benchmark-live`.
Empirical verification on synthetic state (same conditions as the
E2 cold-D pathology):
- OFF (K=0): route fresh session → decode-0 (boilerplate winner)
- ON (K=200): route fresh session → decode-1 (cold D rebalanced)
Validation pass next: scripts/sweep_e3_kvc_v2_loadfloor_rdma.sh
(committed separately).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Implementation jumped ahead of design. The cold-D bonus is one of
several candidates for the overlap-pinning fix (others: load-floor
bonus, idle-D bonus, capacity-aware overlap discount, pre-warming
boilerplate). Need to evaluate the design space first, including
whether a single bonus is even the right shape vs a separate term
in the lex score, before committing to a specific knob.
This reverts commit 786cbb8 cleanly (forensic docs in bf4da28 and
7f2ebf3 are kept since they record observations, not designs).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
KvAwarePolicy now accepts an optional cold_d_bonus int. When > 0,
fresh requests (sticky=0, i.e. no prior D for this session) receive
the bonus added to lex-score position 0 (overlap+sticky_bonus) for
any D worker that has never been assigned a session yet
(decode_assignment_counts == 0). This breaks the pathology
documented in docs/E1_E2_RESULTS_ZH.md §5d where workloads with
shared cross-session prefix (e.g. Inferact's "permissions
instructions" boilerplate) cause every D that has hosted any session
to dominate the overlap term against any cold D, leaving the cold D
permanently unused.
Sticky behavior is preserved: turn 1+ requests of an existing
session continue to stick to their original D because the bonus is
gated on `not sticky`.
Plumbed through ReplayConfig.kvcache_cold_d_bonus (default 0,
keeping current behavior unchanged), BenchmarkConfig, and CLI flag
--kvcache-cold-d-bonus on both `replay` and `benchmark-live`
subcommands. Set above max expected boilerplate overlap (Inferact's
~50 24-token blocks → 1000 is safe).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Replay-side changes paired with the SGLang admission hint:
- DecodeResidencyState gains pause_until_s; admission probe parses
recommended_pause_ms and updates the per-D pause window.
- _wait_for_decode_pause is invoked at request entry points
(_invoke_router, _invoke_session_direct) so requests stall before
hitting a saturated D instead of timing out via mooncake.
- New CLI flags: --enable-backpressure (default off, baseline preserved),
--backpressure-max-pause-s (cap on per-request sleep, default 2s).
Structural instrumentation written under <run_dir>/structural/:
- admission-events.jsonl: every admission probe (RTT, queue_depth,
pause_ms, available_tokens, evicted_count)
- backpressure-events.jsonl: every actual pause sleep
- session-d-binding.jsonl: per-request policy decision
Used to validate the structural claims documented separately.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
v5 dropped errors but pushed session-cap fallback to 46-51%. Before adding
v6 mitigations we need to attribute that capacity loss to one of:
(a) active sessions — real footprint
(b) idle-evictable sessions — LRU not aggressive enough
(c) prefill backup blocks / in-flight / fragmentation — release timing
Without this it's all guessing. Plumb a 1Hz poller into replay that hits
each P/D worker's /server_info, captures session_cache + memory_usage, and
writes a per-worker time-series JSONL to <run_dir>/d-pool-timeseries.jsonl.
Off by default (--pool-poll-interval-s 0); v5+profile sweep enables it at
1.0s. Per-tick HTTP cost is ~8 parallel /server_info calls — negligible
relative to the 50min run.
Analyzer (scripts/analysis/analyze_pool_timeseries.py) decomposes each D's
capacity into active_held / idle_evictable / other (= cap-held-avail, the
backup-blocks bucket) / free, and reports session residency churn across
workers as a starvation/thrashing signal.
Mock-tested poller end-to-end (cancellation clean, file flushed, sessions
captured); analyzer validated against synthetic timeseries.
Next: run scripts/sweep_tp1_v5_optD_profile.sh on hardware (~90min), then
analyze results to pick a v6 direction.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Document the iterative debugging from v1 (broken KVC) through v4
(routing fixed + session cap raised), with code-level analysis of
the two main bugs encountered:
1. v2 root cause (mis-diagnosed previously as `allow_local_prefill`):
`--policy default` for KVC mechanism caused replay's round-robin
policy and the PD router's round-robin to diverge, sending requests
with `session_params` to a D worker that did not have the session
open. Resulted in 56-61% truncation with finish_reason
"session id X does not exist".
Fix: use `--policy kv-aware` (sweep_tp1_v3_kvaware.sh) so replay
emits `x-smg-target-worker` and PD router uses consistent_hashing.
2. v3 new bottleneck: `pd-router-fallback-large-append-session-cap`
dominated 52-65% of requests. Root cause was hardcoded
`min(4, ...)` in `_decode_session_soft_cap`. With 7 D workers x 4
sessions = 28 slots for 52 trace sessions, ~24 sessions starved
permanently (bimodal direct-to-D rate of 0% or 99%).
Fix: raise the cap to 16 (replay.py).
Also includes the v3 finding that direct-to-d-session path P50=0.495s
and TTFT P50=0.043s already beats the 8-way DP baseline (0.65s/0.093s)
- the KVC core mechanism works when fallback paths are avoided.
Files:
- docs/KVC_DEBUG_JOURNEY_V1_TO_V4.md: full journey + code location index
- docs/SWEBENCH_EXPERIMENT_{PROGRESS,RESULTS}.md: prior session notes
- scripts/sweep_tp1_v{2,3,4}*.sh: experiment driver scripts
- src/agentic_pd_hybrid/replay.py: cap 4 -> 16, audit fields
- src/agentic_pd_hybrid/pd_router.py: strip session_params from prefill
- src/agentic_pd_hybrid/metrics.py: truncated_request_count
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
